This paper presents an asynchronous implementation of ARM9 processor, AEM32. We introduce an adaptive pipeline structure that makes the pipeline depth dynamically. We employ a parallel processing control based on datapath splitting to execute the instruction fed into the pipeline in parallel when they have different datapath. AEM32 is synthesized using a 0.35-µm CMOS cell library. Simulation results show that our implementation had 2.6 times higher performance than the asynchronous counterpart, AMULET3i. In terms of Et², AEM32 shows 3 times higher efficiency than the other counterpart, ARM966HS.